I wanted to better understand how the bee lab ran these tests so I didn't have to rely on shipping bees to the lab every time I wanted an accurate mite count. It turns out, it's not too difficult to do accurate mite counts yourself using either an alcohol wash (that kills the bees you will use for your sample) or a powdered sugar method (that doesn't kill your bees, but coats them in powdered sugar and allows you to dump them back in your hive.) The "best" method is still a philosophical debate. In our club, we have decided that the alcohol wash is a more accurate method, and killing 300 bees (about a half cup) to know the mite loads in the colony is better than watching the entire hive die a slow death as a result of viruses vectored by varroa.

Broken down to its simplest form, we want to get the number of mites per 100 bees. However, instead of just taking 100 bees (one sample,) we'll take 300 bees (three samples). A level half-cup measuring cup is approximately 300 bees. Since the nurse bees are the ones that are taking care of the brood and usually near the center of the brood nest, these are the bees that would most likely have the most mites on them. When mites emerge from a cell, they will either crawl into another cell that is about to be capped (they know) to start the process all over again, or they will crawl on to the nearest bee and find a tender spot on them to suck on the bees hemolymph. If that bee is a robber... then the mite may be hitchhiking a ride back to another colony. So, it's important to understand the mite levels in ALL of your hives.

Alcohol Wash Standard Operating Procedure (SOP)

Introduction
The purpose of this SOP is to provide the beekeeper with a procedure for analyzing the mite count in their hive(s). This procedure is called an “Alcohol Wash” which has its own specific procedure and analysis techniques and characteristics. It is a proven method that differs from other mite count methodologies such as the “sugar roll”, “sticky board”, etc. Although there are many opinions on which particular mite count method is best, the Alcohol Wash is a statistically accurate and efficient method that can be completed in a short amount of time by the Novice Beekeeper.

Materials

Alcohol Wash Container (SIBA Made*)

Isopropyl Alcohol (8-12oz.)

1/2 cup measuring cup (for scooping the correct number of bees)

Large bowl or small tote (for shaking and scooping bees)

White t-shirt or similar material (an old shirt not your brand new one)

Plastic container (large enough to stretch t-shirt over)

1/4” mesh screen to put over container (the t-shirt lays over the screen)

Container (for pouring the alcohol back into for reuse after completing the test)

Procedure
The procedure requires the beekeeper to gather 1/2 cup of bees for analysis. This is done by removing a frame of bees from the hive (ENSURE THE QUEEN IS NOT ON THE FRAME) and shaking them off in to the large bowl. Once the bees are in the bottom of the bowl, use the 1/2 cup to gather up the sample bees. The number of bees in a level 1/2 cup is approximately 300 bees. Place the bees in alcohol solution which kills both the bees and the mites and begins releasing the mites from the bee’s bodies. The bees are “swished around” in the alcohol to dislodge the mites from the bees. Once the mites are in solution the alcohol is poured over the white t-shirt which “filters” the mites from the alcohol and allows the beekeeper to accurately count them. After an accurate count is made the beekeeper can then decide the next course of action.

Step 1- Prepare the Alcohol Wash KitPour the alcohol into the alcohol wash container so the alcohol level is about half full. It needs to be full enough to thoroughly cover the bees. Place the screen over the plastic container and place the white t-shirt over the screen. The screen provides support for the t-shirt when the alcohol is poured over the t-shirt.

Step 2- Obtaining the sample bees
Open the hive and retrieve 1 frame of bees. The frame should consist mostly of “capped” and ready to be capped (larger larva) brood. REMEMBER MAKE SURE THE QUEEN IS NOT ON THE FRAME. Take your time and carefully inspect the frame, looking in all the “nooks and crannies” to ensure the queen isn’t hiding. You want to make sure you don’t accidentally kill your queen.

Step 3- Shaking the bees and gathering the 1/2 cup
Take the frame and hold it over the large bowl. Vigorously shake the bees off of the frame and into the bottom of the bowl. Place the frame to the side because you have to act quickly to scoop up the sample bees before they can fly away.

Step 4- Pouring the samples into the alcohol
Using the 1/2 cup, scoop up a level cup of bees and dump them into the alcohol. This step kills the bees. Some beekeepers do not like this step. However, it is better to kill 300 bees to obtain an accurate sample than to kill an entire hive because you don’t have an accurate sample. The alcohol wash test has greater advantages over other testing methods for precisely this reason. The beekeeper knows “EXACTLY HOW MANY BEES ARE IN THE SAMPLE”. The sugar roll or sticky board methods DO NOT allow the beekeeper to know how many bees were sampled.

Step 5- Obtaining the Sample
Put the top on the alcohol wash container and vigorously shake the bees that are in the alcohol. This step dislodges the mites. Once the bees have been shaken for a minute or so, remove the cover. Pull the container (inner container) with the bees in it out of the container (outer container) with the alcohol. Tap the inner container with the bees against the outer container to help shake the mites into the alcohol. The outer container with the alcohol contains the mites.

Step 6- Counting the Mites
Pour the alcohol containing the mites over the white t-shirt, ensuring that no mites remain in the container. Begin carefully counting the mites. Make sure that you don’t accidentally count a “bee part” as sometimes “bee parts” can look similar to mites. Also check around the wire mesh of the inner container to ensure that no mites are caught around the edges. You want to ensure the most accurate count possible.

Analysis
Now that you have an accurate count, it’s time to do some math. Since you started with approximately 300 bees, divide the number of mites you counted by 300 and multiply by 100. Eg if you have 10 mites then 10/300= 0.3X100= 3 mites per 100 bees. It was suggested that if you have brood then you need to double that number as most mites are in the brood cells.

Conclusions
The prevailing wisdom concerning the number of mites per 100 bees that constitutes a threat is anything over 2 mites per 100 bees (6 mites per sample) If you have 2 or more mites per 100 it’s time to think about treating. It is true that mites impact the hive differently throughout the beekeeping season. For example, it is possible that the bees could out breed the mites during the spring buildup. However, once the bees start to slow down, then the mites will eventually overpower the bees and take hold to destroy the colony. The bottom line is to treat your bees against mites as soon as possible in order to protect the investment you have worked so hard to build up. If you were to look at the cost to treat vs the cost to replace a strong hive, it’s about $12
compared to $500, depending on your treatment method.

2 Responses

[…] Varroa mites will peak in July-August. So it’s a good time to evaluate your mite levels and decide on your method for controlling them if it is needed. The Purdue University Bee Lab suggests the following 'rule of thumb' for determining if you mite load load is too high: 50 or more mites drop on a sticky board in a 24 hour period or 5 mites per 100 bees are found using a sugar shake or alcohol wash. […]

A recent-ish test between sugar rolls by Dr. Meghan Milbrath and alcohol wash by Randy Oliver resulted in identical counts for both tests. The critical detail which sugar rollers often forget is to let the jar sit in the shade for a few minutes after rolling. That is the time during which the mites fall off. Going straight from sugar-coating to shaking out the mites will undercount.

Good tip. Either method has it's pros and cons, and it's my personal thought that if you decide on your preferred method and stick with it... you will be a better beekeeper. Likewise with the alcohol wash... there is a right and wrong way to do it. The way that you swish, swirl, pull-out, dip back in and swirl does matter when it comes to getting all the mites dislodged. Every mite counts to help you decide when to take action. With practice and consistency on either method, the desired results can be achieved. Thanks for chiming in.